Vav1 is a signal transducer protein expressed exclusively in the haematopoietic system, where it plays a pivotal role in growth factor-induced differentiation and proliferation. Vav1 couples tyrosine kinase signals with the activation of the Rho/Rac GTPases, leading to cell differentiation and/or proliferation. Vav1 was originally detected as an oncogene, but its involvement in human malignancies has not been reported thus far. We report here that Vav1 is expressed in a neuroblastoma cell line, SK-N-MC. Molecular analysis indicated that there are no gross rearrangements or mutations in the Vav1 gene in SK-N-MC cells. Vav1 protein from SK-N-MC cells was similar to wild-type Vav1 in apparent molecular weight, phosphorylation state, and ability to associate with active EGFR. We also analysed the expression of Vav1 in 42 specimens of human neuroblastoma. Vav1 was expressed in the majority of these tumours. Our results suggest that Vav1 may play a role in the neoplastic process in a subset of neuroblastomas. Copyright 2003 John Wiley & Sons, Ltd.